Lampholder seal

In a lampholder for a lamp having an annular sealing surface, the lampholder comprising a socket having means for making electrical connection with a lamp inserted into the socket and an annular groove in a planar face of the socket aligned opposite a sealing surface of a lamp inserted into the socket;

• and a sealing ring arranged in the groove, said ring having a front surface protruding from the groove for engagement by the lamp sealing surface,
• the improvement wherein said groove is an undercut groove having a first annular width in an undercut portion and a second annular width less than said first annular width at an annular ridge between the undercut portion and the face of the socket;
• and said ring is an O-ring formed of a resilient material having an annular width at a location disposed in said undercut portion of the groove greater than said second annular width;
• in an unstressed condition said O-ring having a circular cross-section and an annular width at a location corresponding to said annular ridge greater than said second annular width,
• whereby said O-ring has an interference fit in said undercut groove and is deformed by said annular ridge.